The present invention relates to a process for modifying xanthan gum to obtain a xanthan gum having enhanced solubility in saline solution.
Xanthan gum is a naturally occurring high molecular weight polysaccharide and has found a wide scope of uses, particularly as a thickener or viscosity modifier for aqueous based compositions. For example, it has found extensive use in the food, cosmetic and oil industries. The ability of xanthan gum to effectively modify an aqueous solution is directly related to its solubility in the aqueous medium. Since in such uses, the aqueous compositions generally contain sodium chloride or other salts, it is desired that the xanthan gum have as high a solubility in such salt solutions as possible. However, xanthan gum which is conventionally obtained from the fermentation of Xanthomonas campestris does not exhibit a particularly high solubility in saline solution, and in particular, saline solutions having relatively high salt concentrations.
A process for obtaining a modified xanthan gum which exhibits enhanced solubility in aqueous solutions of salts, such as, sodium chloride, is disclosed in U.S. Pat. No. 5,416,206. As described therein, and as referred to herein, enhanced solubility means that the xanthan gum exhibits a viscosity of not less than 800 mPa as determined on a 0.5% by weight solution thereof in a 12% by weight aqueous sodium chloride solution at 20.degree. C. at 30 rpm using a Brookfield BL viscometer and having a ratio of this viscosity to that determined on a 0.5% by weight solution thereof in distilled water of not less than 1.5.
This process requires equipment for forming fine fibers of the precipitate while mixing an aqueous solution of xanthan gum with an organic solvent which is a non-solvent to xanthan gum but is hydrophilic. Japanese Patent Provisional Publication Nos. Sho 58-5301(5301/1983) and Hei 1-318001(318001/1989) teach a method for drying xanthan gum directly as precipitated in the form of lumps rather than fine fibers. The dried lumps, despite subsequent grinding, give products sometimes with unfavorably affected properties, such as, low solubility in aqueous saline solutions and other salts. In view of this, there has been need for a way of obtaining xanthan gum of good quality even through the conventional precipitation process.